December 2006
ConradJohnson
Premier 350 Stereo Amplifier: Measurements
All amplifier measurements are performed
independently by BHK Labs. Please click to learn
more about how we test amplifiers there. All measurement data and graphical
information displayed below are the property of SoundStage! and Schneider
Publishing Inc. Reproduction in any format is not permitted.
 Measurements were made at 120V AC line voltage with both
channels driven.
 This amplifier inverts polarity.
 AC line current draw
 Plugged in: 0.02A
 At idle: 1.65A
 Input impedance @ 1kHz: 80k ohms.
 Output impedance at 50Hz: 0.12 ohms.
 Gain (8ohm load): 54.8X, 34.8dB.
 Output noise, 8ohm load, 1kohm input termination, Lch/Rch:
 Wideband: 0.295mV, 79.6dBW / 0.465mV, 75.7dBW
 A weighted: 0.112mV, 88.0dBW / 0.177mV, 84.0dBW
Power output with 1kHz test signal
 8ohm load at 1% THD: 400W
 8ohm load at 10% THD: 500W
 4ohm load at 1% THD: 640W
 4ohm load at 10% THD: 800W
General
The ConradJohnson Premier 350 is a highpower solidstate
design with wide bandwidth and low output impedance typical of solidstate power
amplifiers. It has a complementary MOSFET first stage that provides all the voltage gain
of the circuit. The output stage is a complementary bipolar compound gain of one circuit
with MOSFET drivers. No overall signal feedback is used, although DC feedback is employed
to help keep the outputoffset DC voltage low.
Chart 1 shows the frequency response of the amp with
varying loads. As can be seen, the output impedance, as judged by the closeness of spacing
between the curves of opencircuit, 8ohm, and 4ohm loading, is quite low. The variation
with the NHT dummy load (not shown as it won’t show up in the chart) in the audio
range is of the order of +/ 0.1dB.
Chart 2 illustrates how total harmonic distortion plus
noise vs. power varies for 1kHz and SMPTE IM test signals and amplifier output load. As
can be seen, attainable power is greater for the 4ohm load, as is usual for most power
amplifiers.
Total harmonic distortion plus noise as a function of
frequency at several different power levels is plotted in Chart 3. Amount of rise in
distortion at high frequencies is admirably low in this design.
Damping factor vs. frequency is shown in Chart 4 and is
reasonably constant with frequency.
A spectrum of the harmonic distortion and noise residue of
a 10W 1kHz test signal is plotted in Chart 5. The magnitude of the ACline harmonics is
typical of many power amplifiers measured. The principal signal harmonics are of odd order
with some lowlevel higherorder components.
Chart 1
 Frequency Response of Output Voltage as a Function of Output Loading 
Red line: open circuit
Magenta line: 8ohm load
Blue line: 4ohm load
Chart 2  Distortion as a Function
of Power Output and Output Loading 
(line up at 10W to determine lines)
Top line: 4ohm SMPTE IM
Second line: 8ohm SMPTE IM
Third line: 4ohm THD+N
Bottom line: 8ohm THD+N
Chart 3  Distortion
as a Function of Power Output and Frequency 
8ohm output loading
Cyan line: 350W
Blue line: 70W
Magenta line: 10W
Red line: 1W
Chart 4  Damping Factor
as a Function of Frequency 
Damping factor = output impedance divided into 8
Chart 5  Distortion and
Noise Spectrum 
1kHz signal at 10W into an 8ohm load
